Without limiting the scope of the invention, its background is described in connection with the treatment of Bacillus anthracis infection, one of the first biological warfare agents to be developed and is now perceived as a major threat in the United States, as an example.
Heretofore, in this field, research on the spore forming bacterium Bacillus anthracis has been limited due to its rare occurrence in humans. Infections due to Bacillus anthracis, commonly referred to as anthrax, most commonly occur in hoofed mammals. In humans, the preventive treatment strategy is generally limited to the use of a few antibiotics, including penicillin, doxycycline and fluoroquinolones. (Morbidity and Mortality Weekly Report. 2001. Update: Investigation of bioterrorism-related anthrax and interim guidelines for clinical evaluation of persons with possible anthrax. 50:941-8) While an anthrax vaccine can also prevent infection, the Centers for Disease Control and Prevention (CDC) does not recommend widespread immunization for the general public. (CDC Health Alerts, Advisories, and Updates. 2001. CDC Interim Recommendations for protecting workers from exposure to Bacillus anthracis in work site where mail is handled or processed. Oct. 31, 2000 www.cdc.gov/DocumentsApp/Anthrax/10312001/han51.asp). In fact, vaccination for the general public is not available.
Serious forms of human anthrax include inhalation anthrax, cutaneous anthrax, and intestinal anthrax. Inhalation anthrax is usually fatal. The intestinal disease form of anthrax may follow the consumption of contaminated food and is characterized by an acute inflammation of the intestinal tract. Direct person-to-person spread of anthrax is extremely unlikely, if it occurs at all. Therefore, the CDC explains that there is no need to immunize or treat contacts of persons ill with anthrax, such as household contacts, friends, or co-workers, unless they also were also exposed to the same source of the infection.
For persons infected with anthrax, treatment success is limited by several factors, such as the increased incidence of antibiotic resistance and treatment delays that lessen the chance of survival. It is known that early treatment of anthrax with antibiotics is essential to reduce mortality-delays in treatment profoundly decrease survival rates. Early treatment, however, is difficult because initial symptoms of the infection, e.g., when the bacterial spores are inhaled, heretofore known as inhalation anthrax, may resemble those of the common cold. In addition, symptoms of anthrax infection, depending on how the bacterium is contracted, may take seven to sixty days to appear.
The pathogenicity of B. anthracis is expressed in two ways: a toxic effect made evident by the appearance of an edema, and a so-called lethal toxic effect that may lead to the death of the subject infected. These effects are attributed to the presence of toxins produced by a combination of three protein factors present in B. anthracis. In both humans and mammals, toxins will increase in the body even during early stages of infection when the host appears asymptomatic. This explains why delays in treatment can be fatal. Thus, there is not only a critical need for better anthrax intervention therapies, but a critical need for point-of-care, rapid, and extremely sensitive diagnostic tests to establish the presence of anthrax early in the infection.
Passive immunization in an effort to neutralize toxins with antibodies, usually polyclonal antibodies, has been used as a therapeutic intervention for a variety of bacterial infections (Keller M A, Stiehm E R, Passive Immunity in Prevention and Treatment of Infectious Diseases. Clin. Microbiol. Reviews 13: 602-614). A major limitation of using polyclonal antisera in patients is the possibility of “serum sickness” due to a patient's immune response to proteins derived from a different species. In addition, higher affinity antibodies are more effective for toxin neutralization, but there is no general way to enhance intentionally the affinity of polyclonal sera or even monoclonal antibodies derived from hybridomas.
A general therapeutic method for the neutralization of toxins using high affinity, engineered antibodies or antibody constructs could have application to a wide variety of bacterial infections including native bacterial strains that produce anthrax, diptheria, pertussis, tetanus, and E. coli strains producing Shiga toxin. Pathogenic bacteria of the Australia group such as Brucella abortus, Brucella melitensis, Brucella suds, Chlamydia psittaci, Clostridium botulinum, Francisella tularensis, Pseudomonas mallet, Pseudomonas pseudomallei, Salmonella typhi, Shigella dysenteriae, Vibrio cholerae, Yersinia pestis could also be considered for antibody intervention. In addition, genetically engineered pathogens intended for use as biowarfare agents containing introduced toxins such as Botulinum toxins, Clostridium perfringens toxins, Conotoxin, Ricin, Saxitoxin, Shiga toxin, Staphylococcus aureus toxins, Tetrodotoxin, Verotoxin, Microcystin (Cyanginosin), Abrin, Cholera toxin, Tetanus toxin, Trichothecene mycotoxins, or toxins derived from animal venoms could be neutralized in a similar fashion, leading to dramatically increased survival rates, even for infections in which no vaccine is available.